I needed a frequency reference for tuning up the RS-232 to 100 MHz RF desktop channel adapter elsewhere on this site, when I found this Saronix crystal oscillator in my junk box. A few minutes with AVRStudio produced an ATtiny12 to make a tone – even fewer parts than using an NE-555. With the addition of a transistor to gate the output, I was set to go. Quick and dirty, but it was useful.
For more detail: 100 MHz RF oscillator using ATtiny12 microcontroller
This free embedded project also found using:
- avr 100mhz